In this volume Christopher Tolkien brings to a close the process of bringing together a comprehensive overview of his father's papers. The first half of the book is devoted to the development of the ancilliary matter of The Lord of the Rings, namely the Prologue and the Appendices. These went through a number of stages, with material being added and eliminated. Some parts, such as the "On Hobbits" section of the Prologue, dated back to some of the earliest workings of the novel and were originally extracted from the main text when it became obvious that the digression slowed the flow of the narrative.

In addition, there are an assortment of other papers from the later years of J.R.R. Tolkien's life, mostly scholarly discourses on the nature of the peoples and languages. For instance, there is the account of how the Noldor grew divided about the most euphonious pronunciations of certain sounds, leading to a linguistic division which among humans would take many generations. There are also his thoughts on the problem of the name-element ROS (as in Elros), and of its probable origins. Several times Tolkien established one or another origin, only to subsequently reverse himself and declare that origin impossible and seek another explanation.

In addition to these maunderings on the infrastructure of Tolkien's Secondary World, there are the beginnings of two projected novels which were both abandoned within pages of their beginnings. One, The New Shadow, would have been a sequel to The Lord of the Rings, set several hundred years after those events. However, Tolkien soon abandoned this as lacking in any of the special qualities which made The Lord of the Rings distinctive. The Fourth Age was to be the Age of Men, and Tolkien decided that any story set in that world but dealing only with human characters could be little more than a thriller. The second, Tal-Elmar was to have been a story of the return of the Numenorians to the shores of Middle Earth, as told by one of the peoples who lived there. But the impulse that began it soon failed, and the manuscript runs out without even reaching the point at which the shore folk would have met the Numenoreans.